In the state of the art, marking of objects is known in a variety of forms. Known processes (DE 4126626, DE 4407547, DE 19855623) for the marking of glass utilize, for example, the creation of micro-fissures inside the glass, taking advantage of non-linear processes within the focal range of laser beams to which the glass is transparent. Such micro-fissures scatter and absorb light from the visible spectral range and are therefore visible to man. Due to the formation of local cracks, these processes weaken mechanical stability and are for this reason not advantageous, especially with very thin glass.
No such mechanical damage occurs with the method of ionic color lettering, by which thanks to a locally circumscribed heating of the glass due to the absorption of laser beams, nano-particles of gold, silver or copper are produced within the glass, lending the glass a red color (from gold and copper) or a yellow color in the case of silver. The drawback of these processes lies in the fact that they can only be employed with glass already embedded with gold, silver or copper ions in the melting process (patent disclosure DE 19841547 A1) or in which in a supplemental stage of the process prior to exposure to laser radiation, Na ions of the glass surface are substituted by way of an ion exchange with silver or copper ions from a molten salt bath in contact with the surface of the glass. In either case, the glass must in addition contain ions which when exposed to thermal action reduce the ionic gold, silver or copper to atoms, before the same are separated as nano-particles on account of their limited solubility in glass.
Patent disclosure DE 10119302 A1 describes how the supplemental process prior to exposure to laser radiation can be obviated by placing the portion of the glass surface in need of lettering during the exposure to laser radiation in contact with a silver or copper ion donor medium. In such a case, the processes required for the production of metallic nano-particles lending the color to the glass, the ion exchange and diffusion of silver or copper ions in the glass, their reduction to atoms and aggregation into nano-particles now take place almost simultaneously during the exposure to laser radiation.
Patent disclosure DE 102 50 408 A1 suggests coatings as donor media for silver ions, along with their composition, the processes for the production of such coating compositions and the coating process. The compositions described therein contain at least one silver compound soluble in an aqueous and/or organic solvent and at least one bonding agent. The application of the coating and the required rinse upon completion of the laser radiation are still a drawback, though a less weighty one compared to the complete ion exchange process phase with the molten salt bath.
Patent DE 101 62 119 describes a process wherein, save for the laser radiation, no other steps are needed to apply a durable marking onto a transparent structure. The marking is spaced away from the surface and consists in the mechanically undamaged material solely of a region with a complex refractive index altered vis-à-vis the original state and detectable by optical processes including the naked eye. The changes in the complex refractive index are produced by non-linear optic effects of excitation in elevated power density ranges within the focus of the laser beam, consisting of ultra-short pulses, using for example a Ti:Saphire laser.